Alloy effects in boron doped Si-rich SiGe bulk crystals

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Abstract
We have investigated borondoped Si 1−x Ge x bulk crystals over the composition range 0⩽x⩽0.13 by photoconductivity,photoluminescence, and temperature-dependent Hall effect measurements. Hall effect measurements yield the relation E I =(44.4–108x) meV for the change of the boronionization energy E I with alloy composition. The far-infrared photoconductivity onset caused by the shallow acceptor boron does not shift as much to lower energies with increasing Ge content as previously reported. Transitions that involve excited levels of the shallow acceptor boron are recognizable as a redshift of the photoconductivity onset with increasing temperature. Comparison of the Hall effect data with the shift of the photoconductivity spectra and the evaluation of photoluminescence linewidths give experimental evidence for an inhomogeneous distribution of Ge atoms in the alloy.